Build default jvm core libraries artifacts as modular

#KT-21266

libraries/stdlib/jdk7/build.gradle

@@ -45,9 +45,8 @@ dependencies {
 }
 
 jar {
-    manifestAttributes(manifest, project, 'Main' /*true*/)
-    // TODO: enable as soon as this doesn't cause D8/DX to crash
-    // from sourceSets.java9.output
+    manifestAttributes(manifest, project, 'Main', true)
+    from sourceSets.java9.output
 }
 
 task modularJar(type: Jar) {
@@ -56,7 +55,6 @@ task modularJar(type: Jar) {
     classifier = 'modular'
 
     from zipTree(jar.outputs.files.singleFile)
-    from sourceSets.java9.output
 }